Power receiving device, power supply device, and wireless power transfer apparatus

Abstract

A power receiving device receives alternating current power in a wireless manner from a power supply device including an alternating current power supply and a primary coil. The power receiving device includes a secondary coil, a variable load, an impedance conversion unit, and an acknowledgement unit. Under a situation in which the acknowledgement unit acknowledges that the value of the alternating current power output from the alternating current power supply is unvaried, the impedance of the impedance conversion unit is variably controlled when an electrical property that is dependent on a relative position of the primary coil and the secondary coil varies.

1 . A power receiving device capable of receiving alternating current power in a wireless manner from a power supply device including an alternating current power supply that outputs the alternating current power and a primary coil that receives the alternating current power, the power receiving device comprising:
 a secondary coil capable of receiving the alternating current power from the primary coil;   a variable load having impedance that varies in accordance with a value of input power;   an impedance conversion unit arranged between the secondary coil and the variable load and configured to have a variable impedance; and   an acknowledgement unit that acknowledges a value of the alternating current power output from the alternating current power supply,   wherein, under a situation in which the acknowledgement unit acknowledges that the value of the alternating current power output from the alternating current power supply is unvaried, the impedance of the impedance conversion unit is variably controlled when an electrical property that is dependent on a relative position of the primary coil and the secondary coil varies.   
     
     
         2 . The power receiving device according to  claim 1 , wherein the electrical property includes at least one of transfer efficiency, the value of the alternating current power received by the secondary coil, a value of reflected wave power, and impedance. 
     
     
         3 . The power receiving device according to  claim 1 , wherein
 the impedance conversion unit includes a first impedance conversion unit and a second impedance conversion unit,   the second impedance conversion unit is arranged between the first impedance conversion unit and the variable load and configured to have a variable impedance, and   the impedance of the second impedance conversion unit is variably controlled when the value of the alternating current power output from the alternating current power supply varies.   
     
     
         4 . The power receiving device according to  claim 3 , wherein, when the impedance of the variable load varies, the impedance of the second impedance conversion unit is variably controlled so that impedance from an input terminal of the second impedance conversion unit to the variable load is constant. 
     
     
         5 . The power receiving device according to  claim 1 , wherein
 impedance from an output terminal of the secondary coil to the variable load has a real part including a specific resistance that increases the transfer efficiency to be relatively higher than another resistance, and   the impedance conversion unit performs an impedance-conversion so that the impedance from the output terminal of the secondary coil to the variable load approaches the specific resistance.   
     
     
         6 . The power receiving device according to  claim 5 , wherein the specific resistance is √(Ra 1 ×Rb 1 ) when a virtual load having a resistance of Ra 1  is arranged at an input terminal of the primary coil and resistance from the secondary coil to the virtual load is represented by Rb 1 . 
     
     
         7 . The power receiving device according to  claim 3 , further comprising:
 a fixed load arranged separately from the variable load and having a fixed impedance regardless of the value of the input power; and   a switch that switches an output destination, to which the alternating current power received by the secondary coil is output from the first impedance conversion unit, to the fixed load or to the second impedance conversion unit and the variable load.   
     
     
         8 . The power receiving device according to  claim 7 , wherein, under a situation in which the output destination, to which the alternating current power received by the secondary coil is output from the first impedance conversion unit, is set to the second impedance conversion unit and the variable load, when the electrical property varies while the acknowledgement unit acknowledges that the value of the alternating current power output from the alternating current power supply is unvaried, the switch keeps the output destination, to which the alternating current power received by the secondary coil is output from the first impedance conversion unit, to the second impedance conversion unit and the variable load. 
     
     
         9 . The power receiving device according to  claim 7 , wherein
 when variable control is performed on the impedance of the first impedance conversion unit for the first time from when reception of power from the power supply device starts, the switch switches the output destination, to which the alternating current power received by the secondary coil is output from the first impedance conversion unit, to the fixed load, and when variable control is performed on the impedance of the first impedance conversion unit for the second time or later, the switch switches the output destination, to which the alternating current power received by the secondary coil is output from the first impedance conversion unit, to the second impedance conversion unit and the variable load.   
     
     
         10 . A wireless power transfer apparatus comprising:
 the power supply device; and   the power receiving device according to  claim 1 .   
     
     
         11 . The wireless power transfer apparatus according to  claim 10 , further comprising a control unit, wherein
 the power supply device includes a primary impedance conversion unit arranged between the alternating current power supply and the primary coil,   the primary impedance conversion unit impedance-converts impedance from an input terminal of the primary coil to the variable load so that impedance from an output terminal of the alternating current power supply to the variable load approaches a predetermined impedance, and   under a situation in which the value of the alternating current power output from the alternating current power supply is unvaried, when the electrical property varies, the control unit variably controls the impedance of the impedance conversion unit and the impedance of the primary impedance conversion unit.   
     
     
         12 . A power supply device capable of transferring alternating current power in a wireless manner to a power receiving device including a secondary coil, the power supply device comprising:
 an alternating current power supply that outputs the alternating current power;   a primary coil that receives the alternating current power;   an impedance conversion unit arranged between the alternating current power supply and the primary coil and configured to have a variable impedance; and   an acknowledgement unit that acknowledges the value of the alternating current power output from the alternating current power supply,   wherein, under a situation in which the acknowledgement unit acknowledges that the value of the alternating current power output from the alternating current power supply is unvaried, the impedance of the impedance conversion unit is variably controlled when an electrical property that is dependent on a relative position of the primary coil and the secondary coil varies.